welcome to the garage gocart, there's a buncha firefighters and firetrucks here
if the 42 does have an externally regulated alternator rather than a generator, it's a modification .... yer best bet would be to talk to a good local auto-electric shop, who'd know about the regulator if they can handle a 6v alternator
one thing you might consider is getting the shop to make up an internally regulated 6v alternator, which I had done for a 46, that eliminates the regulator problem and cheaper than both
if the Chev hasn't had other odd changes, it'll be neg ground, the GMCs had pos
Bill
